CLOUDSTACK-7721. Runtime exception while trying to release lock on template_spool_ref.
When a template a copied from a secondary to primary, we were trying to release a lock
twice, once in the create/copy base image function and in the create/copy base image
complete callback routine. This caused the exception as reported in the bug. Fixed by
updating the code make sure we release the lock in copy base image function only as
this is the place we took acquired the lock.